Early Blight
Plant disease · Alternaria solani (a principal causal fungus; Alternaria linariae also causes early blight on tomato)
Description
Early blight is a fungal disease of tomatoes and potatoes. Despite its name, it can develop at any point in the growing season, though symptoms often become most noticeable as plants mature. The fungi survive on infected crop debris and can spread by wind, splashing water, tools, and contact with affected plants. Warm weather and prolonged leaf wetness favor infection. The disease usually begins on older, lower leaves, then progresses upward, reducing the leaf area the plant needs for growth and fruit production. It can also mark stems and, on tomatoes, cause sunken fruit lesions, commonly near the stem end. Potato tubers may develop lesions as well. Repeated infections can cause substantial leaf loss and expose tomato fruit to sunscald. Early blight is more likely to become severe when plants are stressed, particularly by poor nutrition or drought. It is not the same disease as late blight.
Symptoms
- Spots on leaves
- Yellowing leaves
- Leaves dropping
- Rotting fruit
- Stunted growth
How to Identify
Look first at older, lower leaves for dry brown spots that enlarge and often develop concentric rings resembling a target. Yellow tissue commonly surrounds the spots; badly affected leaves turn yellow and die. Stems may have dark, elongated lesions. On tomatoes, fruit lesions are typically dark, sunken, and near the stem, not at the blossom end. Septoria leaf spot usually produces many smaller spots with pale centers and tiny black dots, and seldom affects fruit. Late blight more often causes rapidly expanding, irregular, water-soaked lesions and may produce white growth on leaf undersides in humid conditions. Not every early blight spot shows clear rings, so seek a local diagnostic service if uncertain.
Prevention
Choose resistant or tolerant varieties where available, and start with healthy seed potatoes or transplants. Rotate tomatoes, potatoes, and related crops away from the same bed for at least two years when space permits. Remove volunteer potatoes and tomatoes, and clear infected crop debris at season’s end. Space and support plants so foliage dries quickly. Water at soil level, preferably early in the day, rather than wetting leaves with overhead irrigation. Mulch beneath plants to reduce soil splash. Maintain even moisture and adequate fertility without overapplying nitrogen; stressed plants are more vulnerable. Inspect lower leaves regularly, especially during warm, wet weather. Avoid working among plants while foliage is wet, which can help limit movement of spores.
Treatment
Begin by removing affected lower leaves, provided the plant still has enough healthy foliage. Bag and discard them; do not leave them in the bed. Clean tools after use, and avoid handling plants while wet. Improve airflow by adjusting supports or removing crowded growth, then water at soil level and mulch to limit splash. These steps slow spread but cannot restore damaged tissue. If disease continues to develop, a fungicide labeled for early blight on the specific crop may protect uninfected growth. Options available to home gardeners vary by location and may include labeled biological products or copper-based fungicides. Apply preventively or at the first signs of disease, following the label’s timing, safety, and harvest instructions. Copper can accumulate in soil, so use it sparingly. Remove plants that have lost most of their foliage, and clean up debris after harvest.
Plants Affected
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